This invention relates to metalized elements. More particularly, it relates to metalized elements made from polyester film composites, and more particularly to electrical components comprising wound film capacitors for use in flyback transformer circuits.
Flyback transformers are used in the horizontal deflection circuit for cathode ray tubes (CRT), critical components of computer monitors, and are expected to find significant usage in digital television applications. Commonly used such transformers include elements manufactured by interleaving metalized polyester film with a coated heat sealable polyester film to form coils with an integral resonant capacitor. The coating side is wound against the metalized film and heat-sealed for protection against the corrosion of a final epoxy impregnation. Flyback transformers incorporating wound film capacitors acting simultaneously as resonance capacitors and primary coils are described for example by Okamura in U.S. Pat. No. 5,241,293, incorporated herein by reference. Such flyback transformers have a number of advantages compared to traditional designs involving wire-wound primary coils attached to separate resonance capacitors, including lower space requirements, lower magnetic flux leakage from the outside portion of the secondary coils, and reduction in ringing that otherwise occurs due to undesired resonance between the stray capacitance between the primary coil, and the secondary coil and the secondary leakage inductance.
Film capacitors wound by traditional methods result in an air layer between the film windings. Air layers in these types of high voltage capacitors cause corona discharge resulting in deleterious performance of the dielectric. Traditional wound film capacitors used in flyback transformers thus require impregnation of a resin such as epoxy to eliminate the air layer that exists between the individual film windings. The impregnation step requires a significant amount of manufacturing time to complete which limits the overall production yield. Therefore, elimination of his impregnation step would be advantageous to the high voltage capacitor manufacturer.
Thus there continues to be a need for improved wound film capacitors and methods for their manufacture.
In one aspect of the invention, there is provided an electrical component comprising:
a first elongated dielectric layer having superposed over a first surface thereof a metal layer substantially co-extensive with said first surface and over a second surface thereof opposite said first surface a heat-seal layer coextensive with said second surface;
a second elongated dielectric layer having superposed over a first surface thereof a metal layer substantially co-extensive with said first surface and over a second surface thereof opposite said first surface a heat-seal layer coextensive with said second surface; and
at least one terminal connected to each of said metal layers;
wherein said first and said second elongated dielectric layers are superposed with the heat-seal layer of the second dielectric layer in contact with the metal layer of the first dielectric layer and are wound together to form a substantially cylindrical structure, and wherein each of said dielectric layers and said heat-seal layers superposed thereon has a combined thickness of between about 0.5 xcexcm and about 500 xcexcm and wherein said heat-seal layer constitutes between about 0.5% and about 40% of said combined thickness.
In another aspect of the invention, there is provided a method for making an electrical component comprising:
(a) forming a first metalized element comprising a dielectric layer having superposed over a first surface thereof a metal layer substantially co-extensive with said first surface and over a second surface thereof opposite said first surface a heat-seal layer coextensive with said second surface;
(b) forming a second metalized element comprising a dielectric layer having superposed over a first surface thereof a metal layer substantially co-extensive with said first surface and over a second surface thereof opposite said first surface a heat-seal layer coextensive with said second surface;
(c) positioning said first metalized element over said second metalized element so that said metal layer of said first metalized element is in contact with said heat-seal layer of said second metalized element, and winding both metalized elements to form a generally cylindrical shape; and
(d) applying sufficient heat to said metalized elements to adhere said first and said second metalized elements together; and
(e) providing at least one electrical connection to each of said metal layers.